Method of making a metal coated article with a protective film

ABSTRACT

THE METHOD OF FORMING A PROTECTIVE FILM ON HOT-DIP METAL COATED ARTICLES, AND MORE PARTICULARLY ARTICLES COATED WITH ZINC, BUT THOSE COATED WITH A METAL OF THE GROUP CONSISTING OF TIN, LEAD, ALUMINUM AND ALLOYS THEREOF TOO, BY HOT-DIP COATING AN ARTICLE IN A POT COMPRISING A MOLTEN METAL, DIRECTING A SPRAY OF PAINT DIRECTLY AGAINST THE SOLIDIFIED METALLIC COATING WHILE THE LATTER IS STILL HOT FROM THE HOT-DIP TREATMENT, SAID PAINT COMPRISING FLOWING AGENTS NOT SHOWING ANY BOILING PHENONOMEN AT THE TEMPERATURE THE ARTICLES HAVE AT THE TIME OF APPLYING THE PAINT.

United States Patent Oflice 3,834,933- Patented Sept. 10, 1974 3,834,933 METHOD OF MAKING A METAL COATED ARTICLE WITH A PROTECTIVE FILM Pieter Voogel, Middelweg 144, Wassenaar, Netherlands No Drawing. Filed Oct. 26, 1971, Ser. No. 192,616 Claims priority, application Netherlands, Oct. 29, 1970, 7015901 Int. Cl. C23c 1/00; B44d N14 US. Cl. 117-71 M 3 Claims ABSTRACT OF THE DISCLOSURE The method of forming a protective film on hot-dip metal coated articles, and more particularly articles coated with zinc, but those coated with a metal of the group consisting of tin, lead, aluminum and alloys thereof too, by hot-dip coating an article in a pot comprising a molten metal, directing a spray of paint directly against the solidified metallic coating while the latter is still hot from the hot-dip treatment, said paint comprising flowing agents not showing any boiling phenomenon at the temperature the articles have at the time of applying the paint.

BACKGROUND OF THE INVENTION This invention relates to a method of forming a protective film on hot-dip metal coated articles, and more particularly articles coated with zinc, but those coated with a metal of the group consisting of tin, lead, aluminum and alloys thereof too.

During last years hot-dip metal coated articles and more particularly articles coated with zinc, but those coated with tin, lead, aluminum and alloys thereof too, appeared to be insufficiently protected against corrosion and accordingly such articles have to be provided with an additional protective film.

It has hitherto been proposed to subject hot dip zinc coated articles to a pretreatment, such as hot or cold phosphatizing and subsequently to coat said articles with at least one layer of paint. In this connection the general term paint is intended to comprise paints, varnishes, lacquers, enamels and similar film forming materials.

Said method, executed in several modes, is suffering from the drawback that the pretreatment of the zinc surface that has been eflioresced after a rather short period already is time consuming. Additionally fully drying the zinc surface while preventing its oxidation is diiiicult if not impossible.

Further fresh painted articles require a considerable room for drying, whereas hot drying such as baking or muffiing the paint requires a heating device such as a mufiie furnace and an additional amount of energy.

BRIEF SUMMARY OF THE INVENTION All of the above mentioned drawbacks, arising with conventional methods and with the articles obtained thereby, are eliminated in accordance with the present invention by hot-dip coating an article in a pot comprising a molten metal, directing a spray of paint directly against the solidified metallic coating while the latter is still hot from the hot-dip treatment, and using a paint comprising flowing agents not showing any boiling phenomenon at the temperature the articles have at the time of applying the paint. The flowing agents now will allow the applied paint to evenly spread as a smooth film and will not suddenly and quickly evaporate on contacting the hot articles, which would give rise to holes in the coating.

It will be apparent that the paint components of the paint have to be able to resist the temperature the articles have at the time of applying the paint. Applying the paint while the articles are at a temperature of at least 100 C. is advisable in order to prevent oxidation and deterioration of the metal coating to the utmost as well as to protect it from becoming humid while ensuring a suitable drying or baking of the protective coating.

Preferably a paint is applied comprising a thermosetting resin-based binding agent the curing properties of which being adapted to the temperature the articles have at the time of applying the paint. Examples of suitable thermosetting resins being epoxy resins and alkyd resins.

In a. preferred mode of the invented method the paint comprises a binding agent which will become cross-linked within some minutes at the temperature the articles have at the time of applying the paint in order to enable the thus treated articles to become stacked within a practical lapse of time after the protective film has been applied thereto while preventing the risk of seriously damaging said film.

DETAILED DESCRIPTION OF THE INVENTION The manner by which the invention may be performed is shown by the following illustrative example.

Steel beams having an H section with a length of 4.5 m., a height of 20 cm. and a material thickness ranging from 7 to 13 mm. were hot galvanized as usual by being pickled and subsequently passed through the usual coating pot containing molten zinc covered with a flux layer and being maintained at a temperature of from 420 to 470 C.

The zinc coated beams after emerging from the coating bath cooled down and accordingly the zinc coating solidified. After having arrived at a temperature of about 200 C. said beams were sprayed with a paint of the following composition:

Parts by weight Pigments and fillers 45 Epikote 1001 (Shell) 24 Araldite Harter HY 830 (Ciba) 6 High boiling hydrocarbons:

Solvesso (Esso) 20 Ethyl glycolic ether 5 The paint flowed to an even protective film that quickly dried and became hard. After having further cooled down the beams could become stacked for storage and shipping without running the risk of substantially damaging the protective paint coating.

The thus coated beams were tested for adhesion of the paint coating which appeared to be excellent.

It will be clear that numerous modifications may be made without departing from the spirit of the invention. For example the paint may be sprayed in an electrostatic field. Similar modifications will undoubtedly occur to the skilled worker upon reading these specifications and consequently it is not intended that the invention be limited to the foregoing detailed description that has been given for clearness and understanding only.

While hot dip galvanizing will probably be the most commonly used coating method in this connection, the coating metal does not constitute a limitation on the instant invention which is equally applicable to other hot dip coating methods, such as with thin, lead, aluminum, and similar metals and alloys thereof.

Similarly the method may be used in combination with continuously hot-dip galvanizing or aluminizing of strip steel.

What I claim is:

1. The method of making a protected metal article having a metallic coating with a protective film formed directly on the metallic coating without the aid of pretreatment of such metallic coating, which comprises the steps of:

(a) maintaining a bath of molten coating metal;

(b) dipping the metal article into and withdrawing it from the bath of step (a) to form a metallic coating on the article;

3 4 (c) applying a film forming liquid to the coated surface 3. The method according to claim 2 wherein said therof the article before the article has cooled to a temmosetting resin is an epoxy resin and said selected tem perature less than 100 C., said film forming liquid perature is about 200 C. consisting of synthetic resin binding agent and organic solvent flowing agent in which the flowing agent 5 References Cited ltifitsnalggrhgg pomt temperature substantially greater UNITED STATES PATENTS (d) controlling the point of application of step (e) such 3,155,530 11/ 1964 Schnedler 117105.3 X that the article is of a selected temperature at the 2,861,897 11 1958 Hendrix on 117 105,3 X

point of application in which said selected tempera- 10 3,251,708 5/1966 Schmetterer et al. 11771 M ture is sufficiently lower than said boiling point temperature as to cause said film forming liquid to spread FOREIGN TE evenly as a smooth film without sudden evaporation ,0 938 Great Brltaln 11771 M on ontact; and 480,578 2/1938 Great Britain 11771 M (e) thereafter allowing the article to cool while the 15 film forming liquid dries to form a hard protective RALPH KENDALL, Pflmary Examlnel' film.

A 2. The method according to claim 1 wherein said coating metal is zinc and the article is of steel. 117 114 R, 114 A, 114 B, 114 C, 132 BE, 104 R 

